Electronic transformer control



NOV. 2, 1948. 11 CLARK 2,452,548

ELECTRON I C TRANS FORMER CONTROL Filed March 1, 1944 INVENTOR. DUDLEY B. CLARK ATTORNEYS.

Patented Nov. 2, 1948 UNITED STATES PATENT OFFICE 7 Claims.

This invention relates, as indicated, to an electronic transformer control.

It has heretofore been found advantageous to change the taps mechanically on a transformer winding by various switching connections from either the middle or the end taps by means of an auto transformer connected between the two taps in which it is desired to make the change. This method is slow, laborious and inemcient, and is often dangerous when used in connection with high power equipment.

Another method which has been widely used on small variable voltage transformers involves permitting a high resistance contact to slide over the transformer windings of a circular core transformer. This short circuits at least one turn of the transformer and complicates placing the hand control in a different location from that of the transformer. Moreover, it is not adaptable to high voltages or large power requirements, and also prohibits the use of several turns between transformer taps which increases the short circuit current on the contactor, which, of necessity, is usually of high resistant graphite, carbon brush, or roller.

Moreover, mechanical designs of this type of transformer necessitate expensive construction, compared to ordinary shell type tap transformers.

The present invention has as its primary object the provision of means for obtaining a continuously variable voltage from a transformer, which overcomes substantially all of the disadvantages and objections which characterize the above-described prior methods of voltage control.

Another object of the invention is to provide means of the character described, in which the voltage control is accomplished without short circuiting any of the turns of the transformer at any time, and without opening the circuit between voltage values.

Another object of the invention is to provide control means of the character described, in which the change from one voltage to another is accomplished without any arcing between the contacts, irrespective of the amount of power involved.

Another object of the invention is to provide control means in which voltage changes are'obtained at high speed, with simplicit of operation and without undue wear on the contacts.

Another object of the invention is to provide control means, in which the operator is able to select any number of turns between a fraction of one turn to any multiple number of turns de sired, without being limited to any particular type of material used in the contactors and without making any other changes in the contact mechanism.

A further object of the invention is to provide control means of the character described, in which the operator can vary the voltage on an alternating current line or of a rectified alter nating current voltage of any number of phases, wave forms or ripple percentage.

A further object of the invention is to provide control means which will enable an operator to preset the speed of a machine tool through its motor drive.

A further object of the invention is to provide control means for the purpose of regulating the speed of direct current motors when operated from an alternating current line through rectifying means, by varying the voltage supplied to the armature in either fine or coarse steps, as desired.

A still further object of the invention is to separate and isolate the transformer from the control contacting mechanism, so that the hand control may be installed on a machine and the transformer located at some remote position.

A still further object of the invention is to produce a variable voltage system, in which inexpensive and ordinary transformer construction may be utilized.

A still further object of the invention is to produce a variable voltage direct current from an alternating current source, for the purpose of driving direct current motors, in which the direct current wave form is not distorted by phase shift.

To the accomplishment of the foregoing and related ends, said invention, then, consists of the means hereinafter fully described and particularly pointed out in the claims; the annexed drawing and the following description setting forth in detail certain means and one mode of carrying out the invention, such disclosed means and mode illustrating, however, but one of various ways in which the principle of the invention may be used.

In said annexed drawing, the single figure illustrates more or less diagrammatically a preferred form of circuit embodying the electronic transformer control.

Referring more particularly to the drawing, there is shown an alternate current source, consisting of the lines I and 2, which feed current into an autotransformer T-l This transformer may be either an autotransformer or a portion of an insulating transformer.

A circular contactor, generally designated by ensasas 3 reference R, is also provided, and comprises two annular series of segments of conducting material, an outer series S1, S5, S7, S9, S11, S13, etc., and an inner series S2, S4, S5, S8, S10, S12, S14, etc. The inner segments are in offset or staggered relation to the outer segments, and are insulated from the latter by insulation M, and from the body of the contactor by insulation N. The outer segments are insulated from .each other by segments moi insulatingrnaterial, andthe inner segments are similarly insulated from each other by means of segments n of insulating material. The winding of the transformer T -l is tapped at points 5, 6, 1, 8, 9, 10, H and I2 and point is connected to contact segments S -l andS -Z by line I5, and points 6, l, 8, 9, l 0, ll l2 are connected with contact segments S4, S-5, S-6, S-l, S-8, S9, S--I0 and S! I, respectively, by lines l6, l1, l3, i9, 20, 2| and zarespectively..,, Additional points, not shown, could be established on the transiorrner winding depending, upon the voltages desired, and these points would be connected to additional contact segments of the contactor R similarly to 'the points described. x

Mounted to overlie theico'nt'actor R is 'a con tactor arm, which is revoluble about a shaft S3, and which maybe rotated 3 6(l,de grees. This arm is provided with 'a series of contacts a, A B, and b, spaced longitudinally oijthfe arm and insulated from each other., A series of gridcontactors c is alsojprovid'edoneoi these being jdisposed adjacent each of the insulating segmentsm and a series of gridcontactors ,d is also provided, one of thesebeing, disposed adjacent each of the insulating segmentsn. It will be noted that the insulating Segments and n 'are each slightly wider (the width in acircumferential direction) than the width of the contacts ,or contacting brushes A andlB. The effect of this will be presently considered. o V

Thefcontrol systemiurther includes means for producing, incombination with the transiormer and contactor, avariableyoltage half wave direct urr nt 'sup l ,,.,su, h means. eomleri tiaj n this instance, two electron tubes X l and these being preferablylo'w pressure gas content threeelement grid controlled electron tubes or valves. nn r -qr od t a di ect ,cur ou pu as shown in thedrawing, these tubes are senate through thecontactorft jto the varioustgli oi t n o e T a 1 6 eb'si ionsi flperallel, at other positions in an a ternate zig zag progression, "and in .still otherfpositions that are alternately influenced by a negative. rid shut oft as the powercontactors alternately pass an insulating division. 7 In order to make thisclear, it will beassu'ined that the contactor arm of the contactor R is in the positionshown in thedrawing that is tos'ay, it has moved in a clockwisedirection from the any position wherein the 'power'contacts B have respectively rested on'the conducting segments S1 and S2, The qontactAis still, on the segment s1, which is still the zer position, but the contact B has progressed to conducting segment S4, which is connected wit l i tap #6 'o'n the autotransformer Tl, This is the'firs t voltage position, and, accordingly, 'power will flow through the Wire K and through theltfibe X -,l to terminal a, which is the positive side or the direct current output. The contactorarrn'is new advanced in 'a clockwisedire'ction, an it will be noted that contactor n will reach the's'tationary grid cbfita'ct c, before contact A "reaches the insulating segment between conducting segments S1 and S5. The action which occurs at this point makes tube X2 non-conducting, by virtue of the fact that while contact a, is moving over contact c, a negative grid bias is in effect on tube X2, the grid being able to resume control (on a cycle line) at some portion of each of a second. Ihe tube Xl, however, is conducting andv will carry the load, until contact A is well witl'iin segment S5, at which time contact a will leave contact 0, and the load may now be taken by either or both tubes X-l and X2. Power contact B now approaches the insulating segment between conducting segments S4 and Se, and before it reaches this insulating segment, the contact b will engage contact cl and thereby place a negative bias on the tube XI, as the power contact B crosses the aforesaid insulating seg- Ihent. Contact 1) leaves contact d after contact B has engaged contact Ss.

This condition continues in the manne as described, completely around the circumference of the controller R, and until the'contacts A and B again rest on the segments S1 and S2 respectively, this being the totally off position of the contactor arm.

It will be apparent from the foregoing description, that either or both of the power tubes may be conducting at various points in the movement of the contactor arm, but that neither tube -conducts as the contact A or B'for thepar'ticu'la'r tube to which such contact is connected passes from one conducting segment to another. At'all times, however, there is a continuous flow of power. Due to the difierential in width between the contacts A and B and the insulating segments to which referencehas previously been r'nad'e', "at'no time are any two adjoining sections of the transformer Tl short-circuited.

The controller maybe operated in the reverse or counterclockwise direction with the same progressive results as described, except that "in "this case, the voltage willbe loweredin'ste'ad of raised.

The shaft 83 is "the shaft on which the contactor arm of the controller rotatesand it rsga 'st the conducting path to the grid contact a. The tubes Xl and X-Z are "normally conducting, and either or both -mayconduct, which one eonducts being immaterial except at the position when the grid contacts 0 and d are in use. The number of segments on the controller i'sd'e'per'id out upon the number oftaps with which the transformer Tl is provided-and this "obviously, can be either 'a'la'rg'e ora small number.

As previously explained, the current .throtigh the tubes has a choice of two paths, -and since both tubes are normally conducting, due to the positive bias onthe grids when one tube is extinguis'hed by alternating current "ne ativ g'nd control, the other tube will automaticallypickup the load, so that there is one tube conducting at all times, the tribe's offering an alternate path for the 'power as well as producingrectificatio'n. The transformers -T-'2 and T.--3, which "are shown in the drawing, aregrid transformers.

The grids are shown 'as normally conducting, biased by negative cycle to stop conduction as -the contactors pass the insulating segments. There are numerou other'ways of grid wiring to accomplish this samepurpesa'it beingimi'nateri'al which type of grid connectionjis is-ed. v 4

The 'tap'progre'ssion used in increasing'tlie 'voltage at'the transformer maybe compared, by way ofian'alogy, to arn'an 'clirnbing'a ladder, that 'i's'to say, as'he asce'ndseach step, whileoriefoot passes the otherg-he at no time loses contact with the ladder.

' For extremely fine control of voltage, seldom used except for theadjustment of small fractions of a volt, the low variable resistance Vl is insorted in the output, where required.

In order to produce other types of direct current than that described, it is only necessary to combine the half wave rectifier shown in the drawing with one or more other units of the same, connected in the customary rectifier circuits for producing full wave or any of the polyphase rectifier outputs.

It is also apparent that an alternating current output may be obtained by using two additional tubes reversed, to pass the other half of the cycle.

It is obvious, also, that two or more of the contactors R can be used in a bank with one common shaft extending through the center of all the units, to which a control knob is secured at one end.

It is thus seen that I have provided an advantageous electronic method of producing a voltage control, which may be operated rapidly or slowly as desired, without electrical wear from sparking or loss of efficiency due to shorted turns on the transformer, that continuous contact is maintained while changing taps, and that the controller may be located at a point remote from the transformer.

1 Other modes of applying the principle of my invention may be employed instead of the one explained, change being made as regards the means and the steps herein disclosed, provided those stated by any of the following claims or their equivalent be employed.

I therefore particularly point out and distinctly claim as my invention:

1. In an electric control electronic tube, including a grid, in said circuit for controlling current flow through said circuit; a circuit for controlling said grid; switching mechanism including a plurality of spaced contacts, each contact being connected with a source of electric current of a voltage different from other of said currents, and a contact connected in the first mentioned circuit, said plurality of contacts and said contact being movable relative to one another whereby said contact engages each contact of said plurality of contacts successively and being disengaged from said contacts for an interval between engagement with each succeeding contact; and means for connecting said grid circuit with an electric current source during said interval.

2. In an electric control system; a circuit; an electronic tube, including a grid, connected in said circuit; a circuit for controlling said grid; switching mechanism including a plurality of spaced contacts, each contact being connected with a source of electric current of a voltage different from other of said currents, and a contact connected in the first mentioned circuit, said plurality of contacts and said contact being movable relative to one another whereby said contact engages each contact of said plurality of contacts successively and being disengaged from said contacts for an interval between engagement with each succeeding contact; and means for connecting said grid circuit with an electric current source prior to disengagement of said contact with each of said plurality of contacts.

3. In an electric control system; a circuit; an electronic tube, including a grid, connected in said circuit; a circuit for controlling said grid; switchsystem; a circuit; an

ing mechanism including a plurality of spaced contacts, each contact being connected with a source of electric current of a voltage different from other of said currents, and a contact connected in the first mentioned circuit, said plurality of contacts and said contact being movable relative to one another whereby said contact engages each contact of said plurality of contacts successively and being disengaged from said contacts for an interval between engagement with each succeeding contact; and means for connecting said grid circuit with an electric current source prior to disengagement of said contact with each of said plurality of contacts and for maintaining the last mentioned circuit until after engagement of said contact with a successive contact of said plurality of contacts.

4. In an electric control system, a transformer having a plurality of current output taps; switching means including a set of contacts arranged in spaced relation and insulated from one another, certain of said taps being connected respectively with said contacts, a contact movable in a path over said contacts whereby said contact intermittently engages successive of said contacts throughout a course of movement of said contact, a second set of contacts arranged in spaced relation and insulated from one another, the other of said taps being connected respectively with said second set of contacts, a second movable contact adapted to move in unison with the first mentioned movable contact and over the contacts of said second set whereby said second contact intermittently engages successive r contacts of said second set of contacts, said contacts of said second set of contacts being arranged whereby said second contact is in engagement with a contact during the interval the first mentioned movable contact is passing from one con-- tact to another, and the first mentioned movable contact is in engagement with a contact while said second contact is moving from one contact to another; a pair of electronic tubes, each including a grid; a circuit for passing current through one of said tubes, said circuit including the first mentioned movable contact; a second circuit for passing current through the other of said tubes, said second circuit including said second movable contact; and means associated with said switching means for producing a negative bias on the grid of said one tube prior to disengagement of the first mentioned movable contact with a contact and maintaining said bias until after engagement of said first mentioned movable contact with a successive contact and for impressing a negative bias on the grid of said other tube prior to the disengagement of said second contact from a contact and maintaining said bias until after engagement of said second contact with a successive contact.

5. In an electric control system, a plurality of sources of current having different voltages; a pair of electron tubes, each tube including a grid; means for connecting one of said tubes in circuit with certain of said sources, successively, for establishing circuits of different voltages through said one tube and for connecting the oth r of said tubes in circuit with the other of said circuits, successively, for establishing circuits of different voltages through said other tube, said connections for the first mentioned tube being made during the time a circuit is established through said other tube, and said connections for said other tube being made during the time a circuit is established through the dreams first mentioned nine; and for'estabiisiline ne ative bias on the grids or said tubes rior to the disestablishine'nt "or said circuits for said tubes by the first inentio'ned means and for maintaining said negative bias until 'a 'oonnec tion for a successive circuit has been established by the first mentioned means for said tubes respective-1y.

6; In an electric control system, two electronic grid tubes arranged in aren-e1 wit a load for conducting power to the load; a source of electric power comm-15m a plurality of circuits each of different voltage; two switching mechanisms operable to successively connect said "circuits withs'aid tubes, respectively, sai'd switching mechaniszns each being adapted to provide an interval between each of its successive connections, said intervals occurring only during the time the other of the switching mechanisms is opera tive to establish a connection; grid circuits for biasing the grids of said tubes; and switching devices synchronized with said switching mechanisms for controlling the respective grid circuits and being adapted to render said respective grid circuits operative immediately prior to each interval between said connections of the respective switching mechanisms and to maintain said grid circuits operative until after termination of said intervals.

7. In an electric control system, two electronic grid tubes arranged in parallel with a load for conducting power to the load; a source of electric power comprising a plurality of circuits each of different voltage; and two switching mechanisms, one switching inechaniszn being operable to successively connect certain of said circuits with 8 one of said tubes and the other switching nee-n; anism being operable to connect certain other of said circuits with the otner'drssid tubes, said switchin'g'nie'chanisiiis' each being adaptedto ism: vide an interval between each or its said succes sive connections; said intervals occurring only during the time the other of theswit'ching mech an'isins' is operative to establish a connection; grid circuits for biasing the grids of said tubes: and switching devices synchronized with said switching mechanisms for controlling the respec rive grid circuits and being adapted to rn'der'said respective grid circuits operative immediately prior to each interval between said 'connec'ti'o'ns of the respective switching mechanisms to. to maintain 'sai'd grid circuits operative until after termination of said intervals.

DUDLEY B. CLARK.

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